Android Development Workshop Peter-John Welcome @pjapplez Mobile Engineering Lead 

Day 1 

What we will do Today: Intro: 1. Create our first Android app and run it. 2. Git Crash Course 3. Learn Kotlin for Android 4. Crash Course on Android Layouts. (Constraint Layouts) 5. RecyclerViews (View Holder Pattern) 

Let’s open Android Studio 

Android Dependencies dependencies { implementation fileTree(dir: 'libs', include: ['*.jar']) implementation"org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version" implementation 'com.android.support:appcompat-v7:27.1.1' implementation 'com.android.support.constraint:constraint-layout:1.1.2' implementation 'com.android.support:recyclerview-v7:27.1.1' } 

What is git? 

What is git? ● Git is an example of a DVCS (hence Distributed Version Control System) 

Kotlin 

Google announced Kotlin will be an official language for Android 

Why Kotlin over Java? ● Java is very verbose. ● Java Code is error prone with all its anonymous inner classes. ● Java lacks modern language features. ● Nullability issues. 

Language Features 

var/val var name : String = "Peter" name = "John" val surname = "Welcome" surname = "Johnson" // val can’t be reassigned 

Number one reason Android Apps Crash? 

Null Pointer Exception 

Nullability var name : String = "Peter" name = null // null can’t be a value on a non-null String var surname : String? = "Peter" surname = null val otherName = surname ?: "" // Elvis operator ( ?? in other languages) 

Classes 

Classes class User { private val name: String private val surname : String constructor(name : String , surname: String) { this .name = name this.surname = surname } } var user = User( surname = "Welcome", name = "Peter") // named arguments 

Data class @Parcelize data class Human (private var name: String, val age: Int) : Parcelable //copy, equal, hashcode, toString var human = Human("Peter",27) 

Sealed Classes sealed class Result{ data class Success (val value : T) : Result() data class Error(val error : MyError) : Result() } 

Sealed Classes fun resultsFromService(result : Result) : String { when (result) { is Result.Success -> "${result.value} World" is Result.Error -> return result.error.toString() } return "" } resultsFromService(Result.Success("Hello")) 

Functions 

First class citizens 

High order functions 

Functions fun hello(){ print("Hello") } val functionAsVariable = hello() val greetingPeter = fun (func : (name :String) -> String ) : String = func("Peter") greetingPeter { "Hello $it" } 

Extension functions 

Extension functions infix fun Int.add (value : Int) = this + value val result = 1.add(1) val result = 1 add 1 //Extension function fun Observable.applySchedulers() : Observable = this.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()) //Usage disposable.add(this.viewModel.createPlant(Plant(name = "Best Plant Ever")).applySchedulers().subscribe ()) 

Function Literals with Receiver 

Function Literals with Receiver inline fun SharedPreferences.edit(action: SharedPreferences.Editor.() -> Unit) { val editor = edit() editor.action() editor.apply() } getSharedPreferences("cache", Context.MODE_PRIVATE).edit { putString("username", "Peter") } 

Async Programming 

AsyncTasks class doAsyncTask(textView: TextView) : AsyncTask() { val innerTextView: TextView? = textView override fun doInBackground(vararg params: Unit?): String? { try { ... return data } catch (e: Exception) { return null } } override fun onPostExecute(result: String?) { super.onPostExecute(result) innerTextView?.text = JSONObject(result).toString() } } 

AsyncTasks 

RxJava disposable.add(viewModel.fetchDashboardPlants() .applySchedulers() .subscribe({ //onNext: ... }, { error -> //onError }) ) fun Observable.applySchedulers() : Observable = this.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()) 

Coroutines internal val background = newFixedThreadPoolContext(2, "background") launch (background) { val result = resultsFromService(Result.Success("Hello")) launch(UI) { this.textView.text = result } } // The async await way val someLongRunningTask = async(CommonPool) { return@async "" }.await() 

Let’s build our app. 

Life Cycles and Resources 

Layouts (Constraint Layout) 

RecyclerView 

RecyclerView 

RecyclerView 

RecyclerView class AnimalAdapter(val items: ArrayList) : RecyclerView.Adapter() { // Gets the number of animals in the list override fun getItemCount(): Int { return items.size } // Inflates the item views override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder { return ViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.animal_list_item, parent, false)) } // Binds each animal in the ArrayList to a view override fun onBindViewHolder(holder: ViewHolder, position: Int) { holder.tvAnimalType.text = items.get(position) } } class ViewHolder(view: View) : RecyclerView.ViewHolder(view) { // Holds the TextView that will add each animal to val tvAnimalType = view.tv_animal_type } 

Slides https://tinyurl.com/ycb3cn7f Workshop Feedback https://bit.ly/2uFagmK